Analysis of reservoir
sediments and sediment budget
Sediment removal for the purpose of reducing internal nutrient loading
requires a predredging analysis of the sediments to determine those areas of
the reservoir with the highest release rates.
This analysis should also
determine the depth in the sediments to which highly reactive or exchangeable
forms of phosphorus and othes nutrients extend.
The methods of Williams _
are recommended for phosphorus.
found in Chen, Keeney, and Sikora (1979).
Release rates should be measured
either in situ (Sonzogni et al. 1977) or with sediment cores in the laboratory
The study should be conducted in a manner that will produce a
map of the reservoir which indicates
areas with high release rates.
Appropriate statistically based sampling techniques should be applied to
ensure that release rates obtained are representative of the areas examined.
For a discussion of considerations required in reservoir sampling and monitor-
Sediment removal should be to depths resulting in a
ing, see Waide (1986).
significant decrease in nutrient release.
There is little value to super-
ficial dredging that leaves nutrient-rich layers exposed.
It is important to know how fast the dredged areas of the reservoir will
refill with silt and organic matter.
If silt loading is high, it may not be
cost-effective to carry out sediment removal.
Establishment of appropriate
land use management techniques or the construction of prereservoir sedimenta-
Or, use of dredged materials
tion basins might be necessary before dredging.
as top soil could reduce costs (see Stout and Barcelona 1983).
Rigler (1980) and Ritchie and
(1985) describe measurement methods for
determining sedimentation rates.
Or, direct measurement of the net suspended
solids income, particularly during storm runoff events, can be made..:
Reservoir sediments in agricultural and industrialized areas may contain
chlorinated hydrocarbon pesticides, oil and grease, heavy metals, and
Dredging can release these materials to the water column
in association with suspended
and thus the presence of contami-
nants must be known before initiating operations.
Mutagenic substances have
been found in reservoir sediments.
and Nelson (1983) and Lower
et al. (1985)
of sediment analysis for mutagenic and toxic
Also, an elutriate test
1988) has been devised